Notes. N is the number of sources with spectroscopic redshift in the Cosmos field from the catalogs listed in Sect. 3.2. We note that the sources from our LBT/LUCI program are not taken into account to estimate the galaxy overdensity. ⟨N⟩ is the average number of sources with spectroscopic redshift in the Cosmos field after excluding the G237 region. δ_gal, and σ_δgal are, respectively, the density contrast and significance of the galaxies in G237 in the given redshift ranges. Extent is the area projected on the sky where the galaxies in the defined redshift ranges are distributed, and V_app the volume obtained by multiplying the extent by the distance along the line of sight given by the redshift range. C is the parameter that takes into account the redshift distortions (see text and Steidel et al. 1998). δ_m is the matter overdensity obtained as described in Sect. 6.1, and used in Eq. (2) to derive the z = 0 halo mass M_h(z = 0) reported in the last column. δ_L(z_obs), and δ_L(z = 0) are the linear matter enhancements at the observed redshift and at z = 0, respectively. An overdensity is expected to collapse when δ_L reaches the collapse threshold δ_c = 1.686 (Percival 2005). Thus only the two substructures, and not the full structure, are expected to collapse by z = 0.